1. Field of the Invention
The present invention relates to a copper alloy having an excellent stress relaxation property, and particularly relates to a copper alloy having a suitable stress relaxation property for connection parts such as automotive terminals and connectors.
2. Description of Related Art
The connection parts such as automotive terminals and connectors are now required to have a performance of ensuring reliability in high-temperature such as in an engine room. One of the most important properties for the reliability in high-temperature is a property of maintaining fitting force of a contact, so-called, stress relaxation property. That is, in the case that stationary displacement is given to a spring-like part comprising a copper alloy, for example, in the case that a tab of a male terminal is fitted in a female terminal by a spring-like contact of the female terminal, when the connection parts are kept in high-temperature such as in an engine room, the parts gradually lose fitting force of the contact with time. The stress relaxation property means a resistance property against such cases.
As copper alloys having excellent stress relaxation property, alloys of a Cu—Ni—Si alloy, a Cu—Ti alloy, and a Cu—Be alloy have been widely known. Since any one of them contains a strong oxidizing element (Si, Ti, Be or the like), they cannot be melted and ingot casted in the air, and consequently, increase in cost is inevitable due to waning productivity.
On the contrary, in a Cu—Ni—Sn—P alloy having a comparatively small amount of additive elements, so-called ingot casting using a shaft-furnace can be carried out, so that large reduction in cost can be achieved due to high productivity. Again in the Cu—Ni—Sn—P alloy, measures of improving the stress relaxation property have been variously proposed.
For example, the following patent literature 1 discloses a method of manufacturing a copper alloy for connector having an excellent stress relaxation property. The manufacturing method is for the Cu—Ni—Sn—P alloy, wherein Ni—P intermetallic compounds are dispersed in a matrix uniformly and finely, so that electric conductivity is improved, and in addition, the stress relaxation property and the like are improved. According to the literature, to obtain desired properties, temperatures at start and finish of cooling in hot rolling, and a rate of the cooling, and furthermore temperatures and time of heat treatment for 5 to 720 min performed during a subsequent cold rolling step are necessary to be strictly controlled.
As a Cu—Ni—Sn—P alloy having stress relaxation property and a method of manufacturing the alloy, the following patent literatures 2 and 3 disclose a Cu—Ni—Sn—P alloy formed as a solid-solution type copper alloy in which precipitation of Ni—P compounds is controlled by decreasing a P content to the utmost. According to this, an advantage is given, that is, the alloy can be manufactured by heat treatment of annealing in an extremely short time without needing a sophisticated heat treatment technique. For example, in the patent literature 3, stabilizing annealing after final cold rolling is performed for 5 sec to 1 min within a temperature range of 250 to 850° C. in a continuous annealing furnace, and each of a heating rate and a cooling rate in the annealing is set to be at least 10° C./sec, thereby the stress relaxation property is improved.
[Patent Literature 1]
Japanese Patent No. 2,844,120
[Patent Literature 2]
Japanese Patent Laid-Open No. H11-293367
[Patent Literature 3]
Japanese Patent Laid-Open No. 2002-294368